1. Field of the Invention
The present invention relates to a tool holder which holds various tools and which is mounted on, for example, a machine tool spindle.
2. Description of the Related Art
A conventional tool holder includes, for examples, a tool holder body for holding tools and a tapered shank mounted on a machine tool spindle or the like. When this tool holder is mounted on the machine tool spindle or the like, the tapered shank is brought into engagement with a tapered hole in the machine tool spindle. At this time, the outer surface (outer boundary surface) of the tapered shank has to be brought into close contact with the inner surface (inner boundary surface) of the tapered hole. Accordingly, the tool holder is structured in such a manner that in order to realize secured close contact (or engagement) of the tapered shank with the tapered hole, the tapered shank is formed with a hollow and is thus capable of diameter contraction by means of elastic deformation, and the tapered shank, the diameter of which has contracted, has the property of returning to the original state after the engagement with the tapered hole. The use of this tapered hollow shank also makes it possible to reduce the weight of the tool holder.
Concerning the conventional tool holder having such a tapered hollow shank, the tool holder body and the tapered shank are normally composed as separate units, and the tool holder is structured in such a manner that a flange formed at one end (on the side opposite to the tool insertion hole side) of the tool holder and a flange formed at one end (on the tool insertion hole side) of the tapered shank are placed side by side and are then joined with bolts.
Examples of a tool holder having such a tapered hollow shank include British Patent Publication No. GB2004478A and Japanese Patent Laid-Open (Kokai) Publication No. HEI 7-96436.
However, since the flanges of the conventional tool holder having the above-described tapered hollow shank are secured by using bolts, if the outside diameter of the tool holder body is larger than that of the tapered shank, it is difficult to place the flanges side by side and it is impossible to join them together.
Moreover, even if the tapered hollow shank can deform elastically, it is difficult to cause the flange to do this, thereby resulting in difficulty in causing optimal elastic deformation of the tapered shank. Accordingly, there is a possibility that it may become difficult to bring the tapered shank into secured close contact (or engagement) with the tapered hole in the machine tool spindle. Therefore, it is sometimes necessary to notch the tapered hole of the machine tool spindle or to notch the flange of the tapered shank.
The aim of the present invention is to improve the above-described conventional tool holder. It is an object of this invention to provide a tool holder which allows a tool holder body to be coupled to a tapered shank even if the outer diameter of the tool holder body is larger than that of a flange of the tapered shank, and which is hardly influenced by centrifugal force generated at the time of high-speed rotation, and which can cause elastic deformation of the tapered shank effectively.
In order to achieve this object, this invention provides a tool holder comprising: a tapered hollow shank mounted on a machine tool spindle; and a tool holder body coupled to the tapered shank; wherein the tapered shank and the tool holder body are coupled to each other in the state where a part of the tapered shank is inserted into the tool holder body.
Since in the tool holder having the above-described structure the tapered shank and the tool holder body are coupled to each other in the state where a part of the tapered shank is inserted into the tool holder body, even if the outside diameter of the tool holder body is larger than that of the tapered shank, it is possible to couple the tool holder body to the tapered shank. Moreover, since thick flanges or the like which are used in the conventional tool holder and which hardly deform elastically are not used in this invention for the coupling of the tapered shank and the tool holder body, it is possible to effectively cause the elastic deformation of the tapered shank. Therefore, the tapered shank also has a damping effect. Furthermore, since the tapered shank and the tool holder body are securely coupled to each other, even if, for example, centrifugal force generated at high-speed rotation acts on them, such centrifugal force will have no adverse effect on the integrated state of the tapered shank and the tool holder body.
A coupling part for coupling the tool holder body to the tapered shank can comprise a guiding part for positioning the tool holder body relative to the tapered shank and an attaching part for attaching the tool holder body to the tapered shank.
The guiding part can be located on the tapered shank insertion side of the tool holder body, and the attaching part can be located at a position on the inner surface of the tool holder body further away from the tapered shank insertion side compared to the guiding part. With this structure, the attaching part can be located at a position at a maximum distance from the part of the tapered shank to be placed in a tapered hole formed in the machine tool spindle. Accordingly, it is possible to cause the elastic deformation of the tapered shank more effectively.
The attaching part can comprise: a first screw part formed on the inner surface of the tool holder body, and a second screw part formed on the outer surface of the tapered shank for engaging with the first screw part.
Moreover, the attaching part may be fixed by means of, for example, welding, brazing, or bonding, to secure the inner surface of the tool holder body and the outer surface of the tapered shank, both of which constitute the attaching part.
It is possible to construct the tool holder by using different materials for the tapered shank and for the tool holder body. This makes it possible to bring the tapered shank into close contact with the tapered hole in the machine tool spindle with further certainty even if great centrifugal force is generated at the time of high-speed rotation of the machine tool spindle.
Furthermore, it is possible to employ the setting so that the specific gravity of the material for the tapered shank is greater than that of the material for the tool holder body.
By forming the tool holder body and the tapered shank as separate units, it is possible to manufacture them respectively by using optimal materials.